The present invention addresses a specific problem arising often in middle ear surgery. Numerous causes contribute to ossicular discontinuity including chronic ear disease, congenital aplasia and hypoplasia, and traumatic injury. The location of the incus predisposes it to damage from cholesteatoma. The long process of the incus is most frequently fractured in cases of temporal bone trauma. Additionally, the incus is the ossicle which is most likely to be congenitally hypoplastic or even absent. For the above reasons, ossicular discontinuity secondary to an incus deficiency is one of the most commonly encountered conditions requiring middle ear surgery.
Designs for incus replacement prostheses (IRPs) derive from attempts to sculpt homograft incudi into one of two configurations: the major columellar strut and the minor columellar strut. The term “columella” refers to the resemblance of the resulting ossicular connection to the avian middle ear system. The terms “major” and “minor” refer to the residual structure of the stapes, the final bone in the ossicular chain. If the superstructure of the stapes has been retained, only a small gap exists from the malleus to the capitulum of the stapes and therefore a “minor columellar strut” design can be used to bridge this gap. If the superstructure has been eroded and only the footplate of the stapes remains, a “major columellar strut” would be needed to bridge the larger gap from the malleus to the capitulum of the stapes.
Currently available middle ear prostheses are inadequate to remedy the specific problem of a lateral relationship of the stapes capitulum to the malleus, necessitating a cartilage graft, which has poor sound conductive properties.
The incus replacement prostheses designs available at present do not address two frequently encountered geometric inconveniences. The first problematic geometric relationship is that of a medialized malleus. Years of chronic eustachian tube dysfunction generate negative middle ear pressure, which predisposes ears to developing cholesteatoma. Collapse or atelectasis of the tympanic membrane induces long-term changes in the length of the tendons & ligaments of the malleus, including the tensor tympani tendon. The tendons and ligaments shorten, moving the malleus medially. The cumulative effect of this change in the position of the malleus is to narrow the space between the umbo and the promontory, such that the “head” of the incus replacement prostheses can become trapped in that narrowed space. Trapped between the umbo and promontory, no vibration of the incus replacement prostheses head is possible, and a conductive hearing loss is the result.
The second problematic geometric relationship is related to the first, but conceptually it is useful to consider it as a more lateral relationship of the stapes to the malleus. When this configuration is encountered, we lose the optimal angle required to allow the prosthesis to “stand up” on the stapes capitulum in order to contact the malleus. This can make it impossible to employ a prosthesis, and a material with poor vibratory properties, such as a cartilage graft, may become necessary. With some incus replacement prostheses, the change in the angle relationship of the stapes capitulum to the malleus may bring portions of the prosthesis into undesirable contact with the tympanic membrane, predisposing the tympanic membrane to erosion, perforation, and eventual prosthesis extrusion.
Accordingly, what is needed in the art is an improved incus replacement prosthesis that overcomes the problems associated with the incus replacement prostheses currently known in the art. It is desirable to have an incus prosthesis that accommodates changes in the lateral relationship of the stapes to the malleus and that is adjustable relative to the medial location of the malleus.